The antenna field is well-developed, and various techniques are well-known providing desirable qualities in various types of antennas. The typical goal in any antenna or antenna array is to achieve maximum resolution. Two well-known techniques for increasing resolution in antenna arrays are increasing the frequency of the radiated energy and/or increasing the aperture, or dimensions, of the array.
A number of practical factors limit the extent to which these parameters can be varied. For example, the frequency can be increased to such a point that clutter and rain attenuation significantly degrade the practical resolution of the antenna. Likewise, increasing the dimensions of the antenna can result in practical problems of transporting the antenna (if it is designed to be portable) or supporting it mechanically (regardless of whether or not it is intended to be portable). The same two parameters have further significant effects in that they tend to increase the distance from the antenna at which it is generally considered to be focused, i.e., the far field. In some products which are on the market, the near field comprises a major portion of the useful range. In the near field, or closer to the antenna than the beginning of the far field, linear arrays have azimuth resoluton which is on the order of the antenna aperture dimension. In many applications, such as long range search radar, this deficiency is not at all significant. On the other hand, in other applications, for example, surveillance radar, this deficiency is extremely significant since it means that the surveillance field is, in effect, limited to the antenna's far field, and in the near field, the antenna will not "see" objects intended to be located which may be smaller than the antenna's resolution. For example, in a surveillance radar which is intended to detect relatively small objects such as human beings, bicycles, automobiles or boats, a linear array whose aperture is 30-40 feet in length, may not detect such objects in the near field.
Accordingly, it is one object of the present invention to provide a quasi-linear antenna array which provides excellent resolution and significantly provides that resolution in the near field, as well as in the far field. It is a further object of the present invention to provide an antenna array which is focused in the near field and accordingly provides excellent resolution over a relatively wide range of frequencies. It is another object of the present invention to provide a quasi-linear antenna array having an aperature or dimension on the order of 30-40 feet, but which at the same time, has resolution on the order of 2 feet in the near field